The present disclosure relates to a subject matter contained in Japanese Patent Application No.2001-165403 filed on May 31, 2001, which is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a knocking control apparatus used preferably in ignition timing control of an internal combustion engine, etc.
2. Description of the Related Art
The spark ignition internal combustion engine can get the higher output if the compression ration of the mixed gas is increased higher. In this case, if the compression ration is increased, sometimes the unburned gas is burst up prior to the flame during the propagation of the flame in the cylinder after the spark is sent off into the mixed gas being sucked into the cylinder, i.e., the so-called knocking occurs. If the knocking occurs in the internal combustion engine, not only the engine operates irregularly because the pressure is applied irregularly to the piston but also the engine temperature is increased to lower the thermal efficiency, so that the engine output is lowered. Therefore, in the internal combustion engine, it is decided whether or not the knocking is occurring and then the control to suppress the knocking occurrence is executed by adjusting the ignition timing, for example, if the knocking is occurring.
There is the method that the knock sensor made of the piezoelectric element, or the like is provided in the cylinder and then the decision of the knocking in the internal combustion engine is carried out based on the output of the knock sensor. When the spectrum of the output of the knock sensor is picked up, the output sensed when the knocking occurs becomes larger than that sensed when the knocking does not occur. The difference between the output obtained when the knocking occurs and the output obtained when the knocking does not occur is not uniform over the full frequency of the output of the knock sensor, and appears prominently at the particular frequencies. The frequency at which the difference of the outputs appears remarkably is called the resonance frequency.
The knock sensor whose sensing range is limited only to the resonance frequency band in which the difference of the outputs is large is called the resonance-type knock sensor. In the resonance-type knock sensor, the particular frequency is decided previously by the setting of the sensor itself. That is, the resonance frequency is identified/set to the frequency band, in which it is roughly predicted that the difference of the outputs is increased commonly, at the sacrifice of the characteristics, which are different every cylinder of the internal combustion engine, the states such as the engine speed, etc., and the S/N ratio. Therefore, such resonance frequency of the resonance-type knock sensor employed in the mass-produced same-type internal combustion engine is set equal. However, as described above, the resonance frequency is different every type of the internal combustion engine, and is different based on the engine speed of the internal combustion engine and the individual cylinder of the internal combustion engine. As a result, the resonance-type knock sensor, whose resonance frequency is uniformly fixed, cannot sense the knocking, which occurs in the case that such resonance frequency is not suited to the cylinder, the rotation speed, etc., with good precision.
Therefore, the flat sensor in which the frequency of the knock sensor is not fixed to the particular frequency is employed such that the setting of the flat sensor itself can be changed every type of the internal combustion engine, every engine speed, and every cylinder, i.e., the different resonance frequency can be set every flat sensor. However, since the resonance frequency being set once in one flat sensor is fixed in such flat sensor, the resonance frequency set in one flat sensor is deviated from the frequency at which the knocking occurs even if such frequency at which the knocking occurs is varied due to the time-dependent change, etc. As a result, the knocking cannot be sensed with good precision. That is, there is the problem that, even if the flat sensor is employed, the knocking cannot be sensed continuously for a long term with good precision.
The related art for overcoming this problem is disclosed in Patent Application Publication (KOKAI) Hei 8-177697, for example. According to this related art, the standard deviation is calculated in the level distribution of the output of the knock sensor, then the standard deviation is compared with the predetermined value, then it is decided that the resonance frequency is deviated if the standard deviation is below the predetermined value, and then the knocking sensing precision can be improved by correcting the resonance frequency.
This related art has following problems. The knocking decision period, i.e., the time point and the period to start the extraction of the output of the knock sensor, is fixed every knock sensor. Therefore, since the knocking occurring timing is shifted in the cycle of the internal combustion engine with the time-dependent change of the internal combustion engine, in some cases the output of the knocking is positioned on the outside of the knocking decision period, and thus there is the problem such that the knocking cannot be sensed.
Also, in the cycle of the internal combustion engine, there is the phenomenon such that the vibration is generated at the ignition timing, the seating timing of the suction and exhaust valve, etc. based on the causes except the knocking. These outputs of the vibration by the knock sensor due to the ignition timing, the seating timing of the suction and exhaust valve, etc. are the noises that act as the trouble in sensing the knocking. Because the knocking occurring timing is shifted, there is the case where both the output of the vibration due to the knocking and the noise are contained in the knocking decision period. If both the output of the knocking and the noise are contained in the knocking decision period, it is difficult to discriminate the output of the knocking from the noise. Thus, there is the problem such that the knocking sensing precision is lowered.
It is an object of the present invention to provide a knocking control apparatus for an internal combustion engine, capable of correcting a knocking decision period so as to respond to a variation in a knocking occurring timing and also achieving an excellent knocking sensing precision.
The present invention provides a knocking control apparatus for an internal combustion engine, having a knock sensor for sensing a knocking of the internal combustion engine, a crank angle sensor for sensing a rotation angle position of a crank provided to the internal combustion engine, a setting unit for setting a decision period in which an output of the knock sensor is extracted to decide whether the knocking occurs in response to an output of the crank angle sensor, a storing unit for storing the decision period, a changing unit for changing the set decision period to contain the output of the knock sensor in response to the knocking with a situation in which the knocking occurs, a calculating unit for calculating a difference between the decision period, which is changed to contain the output of the knock sensor in response to the knocking, and the decision period, which is stored in the storing unit, and a correcting unit for correcting the decision period stored in the storing unit in response to an output of the calculating unit to reduce an absolute value of the difference.
According to the present invention, the previously-set decision period can be changed by the changing unit to contain the output of the vibration generated by the knocking, and also the difference between the changed decision period and the decision period stored in the storing unit is calculated and then the decision period stored in the storing unit can be corrected based on the calculated result. According to this, even if the knocking occurring timing is varied in the cycle of the internal combustion engine, the decision period can be changed to respond to the knocking occurring timing and thus the knocking can be sensed with good precision. Also, since the decision period stored in the storing unit based on the decision period that has been changed to respond to the knocking occurring timing, can be corrected, the corrected decision period that can answer to the knocking occurring timing with good precision can be employed to sense the knocking when the internal combustion engine is operated under the same conditions.
Also, in the present invention, the decision period is a time point t1, which is defined in a cycle of the internal combustion engine, and a period w1, which lapses from the time point t1 as a starting point.
Also, according to the present invention, the decision period consists of the time point t1 and the period w1 decided in the cycle of the internal combustion engine, and the decision period can be set or changed by selecting any one or both of the time point t1 and the period w1 so as to respond to the knocking occurring timing. Therefore, the improvement of the knocking sensing precision can be achieved.
Also, in the present invention, the time point t1 is defined differently every cylinder of the internal combustion engine. The time point t1 is defined to be lagged in the cycle of the internal combustion engine as an engine rotation speed is increased higher. The time point t1 is defined to be lagged in the cycle of the internal combustion engine as a fuel injection quantity is reduced smaller.
Also, according to the present invention, the time point t1 of the decision period is decided every cylinder of the internal combustion engine in response to the operation conditions such as the engine speed, the fuel injection quantity, etc. According to this, even if the operation state is different every cylinder, the decision period is set respectively to respond to the timing at which the knocking occurring frequency is high. Therefore, the improvement of the knocking sensing precision can be achieved.
Also, the present invention provides the knocking control apparatus, further having deciding unit for deciding whether the output of the knock sensor contains a noise that is a sensed output of a vibration other than a vibration that is generated by the knocking. If the output of the knock sensor contains the noise, the changing unit changes the decision period in response to an output of the deciding unit.
Also, in the present invention, the deciding unit calculates number of a peak value of the output of the knock sensor, which exceeds a predetermined decision level, in the decision period. The deciding unit decides that the output of the knock sensor contains the noise if the number of the peak value exceeds a predetermined decision value.
Also, according to the present invention, the deciding unit for deciding whether or not the output of the knock sensor contains the noise, based on the number of the peak value of the output of the knock sensor that exceeds the predetermined decision level, is provided, and the decision period is changed in response to the output of the deciding unit. According to this, since it can be decided whether or not the knocking occurs, based on the output of the knock sensor that does not contain the noise within the decision period, the knocking sensing precision can be improved. Also, since the noise deciding unit can be attained by the simple structure and there is no necessity to provide the noise sensing device separately, the size reduction of the system and the suppression of the production cost can be achieved.
Also, in the present invention, the calculating unit further calculates a difference between the decision period changed by the changing unit and a predetermined value. The changing unit changes an after-changing decision period to a before-changing decision period in response to the output of the calculating unit if the decision period is below the predetermined value.
Also, according to the present invention, if the changed decision period is smaller than the predetermined value, the changed decision period can be changed into the preceding decision period once again. According to this, it is possible to overcome the problem such that the decision period is set too short and thus it becomes difficult to catch the output of the knock sensor within the decision period.
Also, in the present invention, the decision period is a plurality of decision periods. The plurality of the decision periods are set in one cycle of the internal combustion engine.
Also, according to the present invention, plural decision periods can be provided in one cycle of the internal combustion engine. According to this, if a plurality of timings at which the knocking occurring frequency is high are present in the cycle, the decision periods can be decided respectively so as to respond to such plural timings at which the knocking occurring frequency is high. Also, since a plurality of decision periods are provided, the decision periods can be decided to avoid the noise occurring timing. Therefore, the improvement of the knocking sensing precision can be achieved.
Also, in the present invention, the deciding unit counts numbers of the peak value of the output of the knock sensor, which exceeds a predetermined decision level, in each of decision periods set in one cycle of the internal combustion engine. The deciding unit decides based on a sum of the numbers whether the output of the knock sensor contains a noise.
Also, according to the present invention, the presence of the knocking occurrence is decided based on the logical sum of the knocking sensor outputs in plural decision periods. Therefore, the knocking sensing precision can be improved.